Process and apparatus for casting elongated slender lengths of metal



ET AL C June 23, 1959 w. MULLER PROCESS AND APPARATUS FOR 25891294 ASTING ELONGATED SLENDER LENGTHS 03 METAL 3 Sheets-Sheet 1 Filed July 30, 1956 INVENTOR. "Ii/Her elhrlch feId,

Beckfir Uilhelm H BY;

June 23, 1959 w. MULLER ET AL 2,891,294

PROCESS AND APPARATUS FOR CASTING ELONGATED SLENDER LENGTHS OF METAL Filed July 30, 1956 3 Sheets-Sheet 2 N M N N 0 i H I i H I I f I f l o I I l H \v H I I II II 0W1 N) I Q) k pk INVENTOR. Wilhelm Mil'll",

Heinrich Korhfeld Ml GofThoH Becker I 75 x404 6 m June 1959 w. MULLER ET AL PROCESS AND C 2,891,294 APPARATUS FOR ASTING ELONGATED SLENDER LENGTHS OF METAL 3 Sheets-Sheet 3 Filed July 30, 1956 r' r green mMw e m 2 f Vmhu W. arm M mfl R M d G ea h v B nited States Patent fice 2,891,294 Patented June 23, 195i);

PROCESS AND APPARATUS FOR CASTING ELON- GATED SLENDER LENGTHS OF METAL Wilhelm Miiller, Duisburg-Hamborn, Heinrich Kornfeld, Dortmund-Horde, and Gotthold Becker, Dortmund- Wambel, Germany, assignors to August Thyssen- Huette Aktiengeselischaft, Duisburg-Hamborn, and Dortmund-Hoerder Huettenunion Aktiengesellschaft, Dortmund, Germany Application July 30, 1956, Serial No. 600,911 Claims priority, application Germany July 28, 1955 2 Claims. (Cl. 22200.1)

The present invention relates to the art of molding metals.

More particularly, the present invention relates to the casting of elongated slender lengths of metal.

The present application is a continuation-in-part of copending application Serial Number 479,934, now abandoned, filed January 5, 1955, which is in turn a continuation-in-part of application Serial Number 337,408, now abandoned, filed February 17, 1953, both applications being entitled Process and Apparatus for Casting Elongated Slender Lengths of Metal.

In forming long slender lengths of metal it is necessary to roll the metal into its final shape after the metal has been poured into a shape suitable for handling by the rolls. When particularly long slender lengths of metal are required, the pouring of the metal creates great difilculties. In order to avoid handling of large bodies of metal, it has already been proposed to pour long lengths of metal which are then subdivided into lengths convenient for rolling.

One of the objects of the present invention is to overcome the above difiiculties by providing a process and apparatus capable of producing any desired length of metal of suitable cross section for rolling so that the necessity of dividing up long lengths of metal is avoided.

A further object of the present invention is to provide a mold apparatus which may be used to produce any length of metal shorter than the length of the mold.

Another object of the present invention is to provide a process and apparatus of the above type which enables the metal in the mold to be separated therefrom in an extremely short time and before the metal becomes entirely hardened.

Still another object of the present invention is to provide a mold apparatus which is of simple construction and capable of giving long reliable service. i

An additional object of the present invention is to provide a process and apparatus according to which molten metal may be poured in succession into a plurality of molds or groups of molds so that the pouring may be continued with some molds while the metal hardens and is removed from other molds, and in this way a substantially continuous output may be provided.

A still further object of the present invention is to provide an apparatus and process particularly suitable for the pouring of killed steel into a mold.

Also, it is an object of the present invention to provide an exceedingly simple apparatus and process for use with rimming steel.

In addition, it is an object of the present invention to provide a process and apparatus which will eliminate cracks in the surface and pipes in the interior of the solidified metal.

With the above objects in View the present invention mainly consists of a process for casting elongated slender lengths of metal in an elongated mold having opposite open ends, this process including the steps of placing a piston in the mold through one of the open ends thereof and locating the piston in the mold at a predetermined distance from the other open end thereof, pouring molten metal into the mold through this other end thereof so that the molten metal contacts the piston and a wall portion of the mold exending from the other end thereof to the piston to produce a hollow body of hardened metal at this wall portion of the mold, and moving the piston at a predetermined rate along the mold while continuously pouring metal into the same through the hollow body of hardened metal to maintain a quantity of molten metal between the hollow body of metal hardening against the wall of the mold and a body of metal hardening against Also, with the above objects in view, the present invention mainly consists of an apparatus for casting elongated slender lengths of metal, this apparatus including an elongated tubular mold having oppoiste open ends, and a piston movably mounted in the mold to be movable toward one end thereof while metal is poured into the mold through the other end thereof. A means is provided to compress the metal in the mold longitudinally to eliminate cracks at the surface of the metal and pipes in its interior.

The novel features which are considered as characteristic for the inventionare set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 is an elongated, sectional, diagrammatic view of an apparatus for carrying out the present invention;

Fig. 2 is a transverse sectional View of the mold of Fig. 1;

Fig. 3 is an elevational, schematic, cross-sectional view of an arrangement for compressing the metal longitudinally; and

Fig. 4 shows a different embodiment of the arrangement of Fig. 3 for use with lengths of metal longer than those made with the structure of Fig. 3.

As is shown in the drawing, the elongated mold 1 is mounted on a suitable support means (not shown) so as to be maintained in a slightly inclined position. The mold 1 has a hollow wall through which a cooling fluid is adapted to flow, the fluid entering through the inlets 2 i 2 illustrates how the mold 1 is divided alongits length" i into top and bottom parts 'la and 1b each of which has opposite sides diverging from each other as they approach the central" level of the mold to provide the substantially rectangular cross section shown in Fig. 2. The parts la and 1b are held together by any suitable means (not shown) such as clamps or the like.

A piston 7 extends into the mold through the lower open end 6 thereof, and molten metal is poured into the opposite open end 4 of mold 1 from a ladle 8 or the like. A well 5 is connected to and communicates with the entrance end 4 of the mold to guide molten metal from the ladle 8 to the interior of the mold.

Fig. 1 diagrammatically illustratesthe process according to which this structure is. used. The piston 7 is located at the beginning of the process adjacent the entrance end 4 of the mold, as shown in dotted lines. The metal poured into the well 5 contacts the piston 7 and the latter iscontinuously drawn toward the end 6 ofthe mold while the molten metal 11 in the well 5 is maintained at a level above-that ofthe mold 1'.

Fig. 1 illustrates an intermediate stage in the process. Asmayv beseen from Fig. l, a hollow tubular body of solidified metal 10 has formed against the inner mold surface and a dished solidified body of metal 12 has formed againstthe piston 7; The piston 7 is withdrawn toward the end 6 ofmold 1 at-a rate fast enough to maintain between the body 10-of solidified metal and'the body 12 of solidified metal a substantially constant space 13 which is filled with molten metal. In this way thebodies 10 and 12 do not become solidified with each other so that the piston 7 is relatively easyto move, and the molten metal continuously pours through the entrance opening 4 of the mold 1 and through the opening 9 of the hollow body of metal 10 to the space 13 which continuously moves down the mold as the length of bodies 10 and 12 increase. The head of molten metal 11 in well 5 as well as the inclination of the mold renders the piston 7 easier to move and the continuous cooling of the mold aids in producing the solidified bodies 10 and 12 in a relatively short time.

The process and apparatus of the invention permits any desired length ofmetal shorter than the mold length to be made with the same apparatus simply by stopping the piston at a desired point along the mold. With the processand apparatus of the inventionit is possible to pour elongated slender lengths of metal which mayrange in length from 2-20 m., for example, and which may have a cross section, for example of approximately 100 x 100 mm., 180 x 260 mm., or 100 x 350 mm. Up to the present time it has not been possible to case elongated slender lengths of metal having these dimensions.

The invention may be used with any metal such as steel or any alloys of steel or other metals. The temperature of the molten metal must be maintained sufficiently high to give the molten metal a high-degree of fluidity, while the coolingof the moldshould not be too intense so that the hardening takes place gradually, and, moreover, the rate of pouring of the metal must be correlated with the rate of. movement of thepiston. As was mentioned above, the piston should be moved fast enough tomaintain a zone of molten metal between the bodies 10 and 12 f hardened metal, and on theother-handthe piston should be moved slow enoughto avoidany turbulence in the molten metal located in the mold.

The slight inclination of the mold produces a head of molten metal pressing against the piston to make the latter easier to move, although the same results could be obtained with a horizontal mold where the head in the well is maintained atta much higher level than that shown 1n the drawing. Generally this latter arrangement will not be aseconomical-and'as desirable as the arrangement illustrated in the drawing where the mold 1 is slightly inclined.

As is apparent fromFig. 2, the moldcomprises top and bottom. parts 1a and 1b which are removably connected to @flChother in any suitable way along the, length of the v mold. This arrangement permits the cast metal to be very quickly and easily separated from the mold by removing the top part thereof from the bottom part thereof. The positive cooling of the mold causes the outer layer of the cast metal to solidify before the inner molten metal solidifies, and this solidification of the outer layer of metal takes place in a very short time as a result of the cooling of the mold. Therefore, after the desired length of metal is obtained and the movement of the piston is stopped in the mold, the metal in the mold is very shortly in a condition where its entire outer surface is solidified and at this point the mold may be removed because the molten metal still located in the interior of the casting is now surrounded by solidified metal.

Thus, the molds of the present inventon may be separated from the cast metal in an extremely short-time 'so that the molds are not subject to extremely high temperatures for as long a period of time as with conventional molds, and all of these factors permit a relatively small number of molds according to the present inventiontoaccomplish the same results as a much larger number of conventional'rnolds because the molds of thepresent invention may be released from the cast metal in arelativcly short period of time so as to be available for further use and because the molds of the present invention have a much longer life than conventional thick-walled molds.

The molds of the present invention are suitable for producing lengths of metal which are convenient for the normal further processing of the long lengths of metal. If particularly short lengths of metal are required in certain special. cases, these canbe produced. with the apparatus of the invention simply by stopping the piston when the desired short length is obtained. However, it may be uneconomical to stop the operation where several extremely short lengths of metal are required, and in this latter event it is probably better to mold a longer length of metabwhich can then be dividedinto the desired shorter lengths.

A specific example of a process t according to the invention as described above is as follows:

The metal poured was a mild, killed steel which included 0.5% manganese, 0.02% phosphorus, 0.025%

oxygen, 0.025% sulfur, 0.08% silicon, 0.1% carbon, and 0.8 kg. of aluminum per ton of metaL. This metal was.

poured at a temperature of 1530f C. a The cross sectional areaof; the mold was x. mm,, and the length of the metal in the mold at theend of the process was 10 meters. The mold wall was 4 mm. thick and made of a killed Siemens-Martin steel. The piston was moved away from the starting end of the mold at a rate. of 6 meters per minute, and the metal was poured into the well shown in Fig. l at arate sufliciently great to maintain the level of the molten metal at all times higher than the uppermost part of the mold. This required original filling of. the well 5 shown in Fig. 1 up to the level indicated in Fig. l and-then the molten metal was continuously poured into the well 5 substantially at the rate of 0.13 cubic meter per'minute. Thecooling water was;supplied atthe rate of 2.5 cubic meters per minute through the passage in the: wall of the mold, and this.

passage had a total cross sectional area of 8200 square mm. Thus,it will be noted-that with this process in one minute and forty seconds the length of 10 meters of the metal in the mold was obtained, and thuswith the process;

of the; invention themetal is poured into the mold at a relatively quick rate. This relatively fast movement of the piston guarantees that two distinct bodies of solidifying metal are maintained in the mold entirely separate from each other through an intermediate body of molten metal indicated at 13 in Fig. l.

solidify and of course the molten body 13 in' the mold solidifies and unites the two bodies of metal: which are maintained apart from each other by the intermediate molten body, of metal; The temperature of cooling After the piston is stopped, the metal in the mold continues toassua e '3 water of C. was increased to C. after pouring 1 m. length and to C. when the piston was stopped.

Because of the relatively great length of the metal poured into the mold and particularly with substantially horizontal molds as shown in Fig. 1, many cracks form in the surface of the length of metal as a result of the fact that the outer skin of the metal solidifies while the interior thereof remains molten and as a result of the friction between the poured metal and the mold. The formation of these undesirable surface cracks takes place not only after the pouring of the metal terminates but also during the pouring of relativelyl long lengths of metal.

In accordance with the present invention such surface cracks are eliminated by applying to the metal both during and after the pouring thereof an axial compressive force which is sufliciently great to decrease the length of the poured metal.

The compressive force which is at least great enough to overcome the friction between the metal and the mold is applied in such a way that from the beginning of the pouring up to the end of the pouring the compressive force increases at a relatively small rate While at the end of the pouring the compressive force is in- [creased at a relatively larger rate and then as the solidification of the metal progresses the rate of increase of the compressive force is again relatively small.

The compression is carried out according to the length of metal which is poured and according to the particular material which is poured, and in particular according to its shrinking characteristics.

The time required for pouring and solidification is essentially dependent u on the cross section of the metal which is poured.

Any person skilled in the art can determine the proper manner to apply the compressive force when the shrinkage characteristics of the poured metal are known and the pouring and solidification time can be determined in accordance with the particular cross sectional area of the length of metal. It is important that when the compressive force is plotted over the time a substantially S-shaped curve is provided, this curve rising gradually during the beginning of the pouring and then rising steeply during an intermediate part of the entire time of the process which takes place immediately after the pouring terminates, and then the curve again becomes relatively flat and rises gradually during the time that the solidifica- -.tion progresses.

When a length of the before mentioned mild steel equal to 12 meters and having a cross section of 155 x 190 mm. was poured, the entire time during which compression was applied was equal to 10 minutes, and during this time the compressive force caused the length of metal to become shorter by 16 cm. During the first 80 seconds of the pouring the length of metal was decreased 3 cm. and from this point until the end of the third minute the length of metal was increased an additional 9 cm., so that in 10 minutes time the total decrease in length was equal to 12 cm., the actual pouring having terminated at the end of 100 seconds, and the compressive force being applied at a greatly accelerated rate during the time from the end of the first 100 seconds to the end of the third minute. Then the compressive force was applied again at a relatively small increasing rate and from the end of the third minute up to the end of the tenth minute the length of the metal decreased an additional 4 cm., thus producing the total decrease in length of 16 cm., and during the time that the compressive force was applied the total compressive force ranged between 2 and 9 tons to avoid surface cracks.

Referring to Fig. 3 it will be seen that the mold 34 is schematically shown in a substantially horizontal position, and Fig. 3 furthermore shows the piston in the mold which is moved to the left, as viewed in Fig. 3, along the interior of the mold as the metal flows into the latter.

A tubular means 37 directs the molten metal into the interior of the mold through the right open end thereof, as viewed in Fig. 3, and this tubular means has a free end 35 located in the interior of the mold at its right end portion, as viewed in Fig. 3. A cylinder 33 is fixed to the tubular means 37, which is stationary, and this cylinder 33 has a right open end, as viewed in Fig. 3, directed away from the mold 34. A piston 32' is slidable Within the cylinder 33 and can be moved outwardly beyond the right open end thereof, and at its right end the piston 32 is fixed to a suitable framework shown diagrammatically in Fig. 3 and fixed to the right end of the mold 34. A pump 31 which may be operated 'by motor or by hand pumps a suitable fluid such as oil, water, or air, into the interior of the cylinder 33 to urge the piston outwardly of the cylinder to the right as shown by the arrow in Fig. 3, and as a result the mold 34 is urged to the right, so as to tend to locate the free end 35 of the tubular means 37 to a greater extent in the interior of the mold 34.

As was pointed out above, a tubular body of metal forms in the interior of the mold adjacent the end thereof into which the molten metal flows, and this tubular body of metal is indicated at 36 in Fig. 3. As is evident from Fig. 3 the tubular body of metal automatically solidifies with its right end abutting against the left end of the free end portion 35 of the tubular means 37. As a result, with the structure of Fig. 3 an axial compressive force is applied to the tubular body 36 during the time that the molten metal flows therethrough toward the piston which is moving to the left along the interior of the mold 34. Of course, the important factor is that there be between the free end 35 of tubular means 37' and the mold a force tending to provide a relative motion which tends to locate the free end 35 to a greater extent in the interior of the mold 34, and thus it is theoretically possibleto maintain the mold 34 stationary and to urge the tubular means 37 to a greater extent into such a stationary mold, but the arrangement shown in Fig. 3 is preferred because with this arrangement it is unnecessary to move the tubular means 37 which thus can be maintained in line with the ladle from which the molten metal pours without any difliculty. Of course, instead of a hydraulic or pneumatic urging means, it is possible to use an electric motor which through a suitable gear reduction unit operates a spindle which urges the mold 34 to the right, as viewed in Fig. 3, such a spindle being, for example, in threaded engagement with the framework connected to the mold 34 to urge this framework together with the mold 34 to the right, as viewed in Fig. 3.

It has been found that where particularly long lengths of metal are poured, such as metal lengths greater than 10 meters, for example, the compressive force which is transmitted from one end of the length of metal becomes so small by the time it reaches the opposite end thereof that it is desirable to provide in such cases a pair of compressive forces acting axially toward the center of the length of metal from the ends thereof, and a structure for accomplishing this result is illustrated in Fig. 4. As may be seen from Fig. 4, the structure for providing a compressive force on the length of metal from the right end thereof, as viewed in Fig. 4, is identical with that shown in Fig. 3 and described above. Fig. 4 also illustrates diagrammatically the support for the mold which permits the same to move axially. As is evident from Fig. 4 the mold is carried by a pair of tables which rest on rollers which are in turn rollable upon the top surfaces of a pair of base members, so that in this way the mold is free to move axially to the right and left, as viewed in Fig. 4, and the same support structure is used with the embodiment of Fig. 3.

As is shown at the left portion of Fig. 4, the piston 42 which shifts to the left along the interior of the mold 34 during the pouring of the metal is connected to a chain 42' which passes over a pulley which can be manu- 7 ally turned, for example, in order to advance the piston 42 to the left during the pouring of the molten metal. The chain 42 passes freely throughan axial bore in a rigid member 41 which has an enlarged end 41' fixed to a pair of pistons 39. These pistons 39 are respectively slidalble in a pair of cylinders 40 having open ends directed toward the mold 34, and the pistons 39 extend outwardly beyond the open ends of the cylinders 40". The cylinders 4t? are in turn fixedly carried by a rigid plate 38a of a framework 38 which is fixed to the leftv end of the mold 34, and plate 38a is also formed With an aperture through which the chain 42 freely passes. A pump 31' which may be identical with the pump 31 applies any suitable fluid under pressure to the interior of the cylinders 40 to act against the left ends of the pistons, as viewed in Fig. 4, so as to urge these pistons in the direction of the arrow shown in Fig. 4 to the right, and thus the member 41 is urged to the right against the piston 42 to urge the latter to the right. The member 41 together with the pistons 39 and the framework 38 and cylinders 40 remain substantially in the position shown in Fig. 4 during the pouring. At the end of the pouring the piston 42 has been moved to the left up to the position shown in Fig. 4 where it is in engagement with the member 41. However, if the movement of the piston 42 is terminated shortly before it reachesthe element 41, the fluid introduced into the cylinders 40 by the pump 31 will move the element 41 to the right into engagement with the piston 42. When the movement of the piston a2 to the left has been stopped, which is to say when the desired length of metal has been provided in the mold34, the element 41 is urged against the piston 42 With a forcewhich urges the piston 42 to the right, as viewed in Fig. 4, so that in this way compressive forces are applied to the length of metal from the ends thereof acting axially toward its center.

Of course, only one cylinder 40 and piston 39 may be used, or any desired number of pistons and cylinders may be used, and furthermore the pistons may be fixed to the plate 38a and the cylinders may be fixed tothe portion 41 of the element 41 and the same results can be produced. Also, as was described above in connection with Fig. 3, the invention is not limited, to the use of a hydraulic or pneumatic means for providing the compressive force.

The pressure which is used according to the process of the invention is on the order of 400 kg. for each centimeter of the outer periphery of a cross section of the length of metal which is poured, where this length of metal is equal to meters and where its cross section is- 155 x 190 mm.

Experience has shown that when the compressive force applied to the length of metal either from one or both ends thereof is substantially greater than the force re quired to prevent cracks from forming in the surface of the metal, then this compressive force also prevents pipes from forming in the interior of the metal. After the pouring of the metal has terminated the outer surface thereof solidifies while the interior remains molten, and during solidification of the interior of the metal pipes arelikely to form. With the process and apparatus of the invention such pipes are reliably eliminated as a result of the compressive force applied. Thus, where the compressive force is applied only at the right end of the metal, as shown in Fig. 3, the compressive force increases at a relatively small rate until the end of the pouring, and then this compressive force is increased at a highly accelerated rate, and finally as the solidification progresses the compressive force continues to increase at a relatively small rate. In this way the formation of pipes as well as the formation of cracks isprevented. Where the compressive force is applied from both ends, as shown in Fig. 4, the compressive force applied throughthe piston 42 at the left end of the metal, as viewed-irrFig. 4, isonly, applied when the. pouring has terminated, and at this time the compressive force applied through the piston 42 is applied in a manner which corresponds to the application of the compressive force at the right end of the; metal. the pouringhas terminated the compressive forces are applied at, both ends of the length of metal at a relatively greate rate of increase, and then as the solidification progresses further the rate of increase of the compressive force is smaller. Thus, with the embodiment of Fig. 4 which is. used for relatively long lengths of met l both the formation of surface cracks and the formation of pipes are eliminated reliably.

Thus, with the process and apparatus of the present invention it is possible to obtain long slender lengths of metal which are free of surface-cracks and free of pipes in their interiors. These long slender lengths of metal can be used with a minimum of further processing in rolling mills and the like which enable the metal to be formed into suitable sheets, for example. Thus, with the present; invention it is possible to provide almost unlimited lengths of metal which. are completely free of flaws.

It will be understood that each of the elements de scribed above, or two or more together, may also find a useful application in other types of molding processes and apparatus differing from the types described above.

While the-invention has been illustrated and described as embodied in process and apparatus for molding long slender lengths of metal, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will fully reveal the gist of the present invention that. others can by applying current knowledge readily adapt it for. various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of thegeneric or specific aspects of this invention and, therefore, such adaptations should and are intended-to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. Process for casting elongated lengths of metal in an elongated mold having one end closed by a piston axially movable therein, which comprises pouring molten metal into the mold through the open end thereof at a rate sufficient to maintain the mold substantially filled up to the piston, cooling the mold to solidify a dish shaped body of metal at said piston and a tubular body of metal along the mold Wall from the open end thereof toward the piston, while simultaneously applying an axially acting compressive force to said tubular body of solidified metal during said pouring at a first increasing rate which is relatively small, stopping the movement of the piston when the desired length of metal is obtained, immediately increasing the axial compressive force at a second rate substantially greater than said first rate and as the molten metal becomes more solid, increasing the compressive force at a third rate substantially smaller than thesaid second rate.

2. Process for casting elongated lengths of metal in an elongated mold having one end closed by a piston axially movable therein, which comprises pouring molten metal into the mold through the open end therof ata rate suflicient to maintain the mold substantially filled up to the piston, cooling the mold to solidify a dish shaped body of metal at said piston and a tubular body ofmetalalong themold wall from the open end thereof toward the piston, while simultaneously applying to the end of said tubular body of solidified metal adjacent to the open end of said mold an axial compressive force acting longitudinallyalong said tubular body during said pouring, gradually increasing said compressive force at a first relatively. small rate, stopping the piston when the.

Thus, immediately after desired length of metal is obtained, immediately applying through said piston to said metal in said mold an additional compressive force acting longitudinally along said metal in said mold and increasing the compressive force additionally applied through said piston at a second rate substantially greater than said first rate, and simultaneously increasing the compressive force applied to said end of said tubular body at a rate substantially greater than said first rate, and as the metal continues to solidify, increasing the compressive force applied to both ends of the length of metal at a rate substantially smaller than the rate of increase of the compressive force applied immediately after the piston stopped.

References Cited in the file of this patent UNITED STATES PATENTS Billings May 13, 1884 Billings June 9, 1885 Billings et al. Jan. 5, 1886 Illingwotth Apr. 26, 1892 Trotz July 28, 1908 Monnot Dec. 28, 1909 Douteur Dec. 28, 1909 Maxwell May 20, 1913 Pehrson Feb. 24, 1914 Lane Aug. 4, 1925 FOREIGN PATENTS Great Britain Mar. 9, 1955 

